The present invention relates to an encoder, a decoder, a recording medium, a coding method, and a decoding method, more particularly to an encoder, a decoder, recording medium, a coding method, and a decoding method for encoding or decoding images with reference to a reference table.
An image processing apparatus that uses a color look-up table has an advantage to reduce the amount of image information easily by reducing the number of bits assigned to each pixel.
When the number of bits assigned to each pixel is reduced, however, the number of colors that can be displayed is also reduced. This is a problem to arise from such a prior art image processing apparatus.
Under such the circumstances, it is an object of the present invention to solve the problem and enable the information amount of an entire image to be reduced without reducing the number of colors that can be displayed.
An encoder according to the present invention comprises a unit for computing transition information concerning transition of indexes of at least two of adjacent pixels of those forming an image; a unit for creating a reference table by selecting part of the transition information computed by the transition information computing unit by a specified method; and a unit for encoding the image with reference to the reference table created by the unit for creating the reference table.
A method of encoding an image according to the present invention comprises the steps of computing transition information concerning transition of indexes of at least two of adjacent pixels of those forming an image; creating a reference table by selecting part of the transition information computed in the step of computing transition information by a specified method; and encoding the image with reference to the reference table created in the step of creating reference table.
A recording medium according to the present invention is recorded with a reference table created by computing transition information concerning transition of indexes of at least two of adjacent pixels of those forming an image and selecting part of the computed transition information by a specified method, and image information encoded with reference to the created reference table.
A decoder according to the present invention comprises a unit for storing a reference table created by computing transition information concerning transition of indexes of at least two of adjacent pixels of those forming an image and selecting part of the computed transition information by a specified method; a unit for inputting image data compressed with reference to the reference table; and a unit for decoding the image data inputted by the unit for inputting with reference to the reference table stored in the reference table saving unit.
A method of decoding according to the present invention comprises the steps of storing a reference table created by computing transition information concerning transition of indexes of at least two of adjacent pixels of those forming an image and selecting part of the computed transition information by a specified method; inputting the image data compressed with reference to the reference table; and decoding the image data inputted in the step of inputting with reference to the reference table stored in the step of storing reference table.
In an encoder according to the present invention, the transition information computing unit computes transition information concerning transition of indexes of at least two of adjacent pixels of those forming an image, the reference table creating unit creates a reference table by selecting part of transition information computed by the transition information computing unit by a specified method, and the encoder encodes images with reference to the reference table created by the reference table creating unit. For example, the transition information computing unit computes transition information concerning transition of indexes of two adjacent pixels in the horizontal scanning direction on the screen and the reference table creating unit creates a reference table by selecting the information of the upper four appearance frequencies from the transition information computed by the transition information computing unit, and the encoder encodes pixel data forming an image sequentially with reference to the created reference table.
In an encoding method according to the present invention, transition information concerning transition of indexes of at least two of adjacent pixels of those forming an image is computed in the step of computing transition information, a reference table is created in the step of creating the reference table by selecting part of the transition information computed in the step of computing transition information by a specified method, and images are encoded in the step of encoding with reference to the reference table created in the step of creating the reference table. For example, transition information concerning transition of indexes of two adjacent pixels in the horizontal scanning direction on the screen are computed in the step of computing transition information the reference table is created in the step of creating the reference table by selecting information of the upper four appearance frequencies from the transition information computed in the step of computing transition information, and pixel data forming an image are sequentially encoded in the step of encoding with reference to the created reference table.
In a recording medium according to the present invention, there is recorded a reference table created by computing transition information concerning transition of indexes of at least two of adjacent pixels of those forming an image and selecting part of the computed transition information by a specified method, and image information encoded with reference to the created reference table. For example, the recording medium is recorded with a reference table created by computing transition information concerning transition of indexes of two adjacent pixels in the horizontal scanning direction on the screen and selecting information of the upper four appearance frequencies from the computed transition information, and pixel data encoded with reference to the created reference table.
In a decoder according to the present invention, the reference table storing unit stores a reference table created by computing transition information of indexes of at least two of adjacent pixels of those forming an image and selecting part of the computed transition information by a specified method, the input unit inputs image data encoded with reference to the reference table, and the decoder decodes image data inputted by the input unit with reference to the reference table stored in the reference table saving unit. For example, the reference table storing unit stores a reference table created by computing transition information concerning transition of indexes of two adjacent pixels in the horizontal scanning direction on the screen and selecting the information of the upper four appearance frequencies from the computed transition information, and the decoder decodes encoded image data inputted by the input unit to original data with reference to the reference table stored in the reference table storing unit.
In a decoding method according to the present invention, a reference table is stored in the step of storing a reference table, the reference table being created by computing transition information concerning transition of indexes of at least two of adjacent pixels of those forming an image and selecting part of the computed transition information by a specified method, image data encoded with reference to the reference table is inputted in the step of inputting, and the image data inputted in the step of inputting are decoded with reference to the reference table stored in the step of storing reference table. For example, in the step of storing a reference table, there is stored a reference table created by computing transition information concerning transition of indexes of two adjacent pixels in the horizontal scanning direction on the screen and selecting the information of the upper four appearance frequencies from the computed transition information, and in the step of decoding, encoded image data inputted in the step of inputting are decoded to original data with reference to the reference table stored in the step of storing the reference table.